Phenolic compounds

ABSTRACT

A phenolic compound is provided which can be described by the formula ##STR1## in which Ar is a C 6-20  aromatic moiety, L is a cyclohexanenorbornane linking moiety, L&#39; is a divalent cycloaliphatic moiety, and each of m and n is a number within the range of 0 to about 10. Such phenols include the product of the addition reaction of phenol with a cyclohexenenorbornene compound such as 5-(3-cyclohexen-1-yl)bicyclo[2.2.1 ]hept-2-ene.

This is a division of application Ser. No. 013,837 , filed Feb. 5, 1993.

BACKGROUND OF THE INVENTION

This invention relates to novel phenolic compounds. In one embodiment,the invention relates to phenolic curing agents for epoxy resins.

Polyphenolic compounds are useful as curing agents for epoxy resins.When used as a component of an epoxy resin-based electrical laminationformulation, it is desirable for both the epoxy resin and the curingagent to have a low melt viscosity, as formulations which can be appliedto glass fibers in the melt, rather than in solution, are favored.

It is therefore an object of the invention to provide novel phenoliccompounds. It is an object of one aspect of the invention to providepolyphenols which have a low melt viscosity.

SUMMARY OF THE INVENTION

According to the invention, a phenolic compound is provided which can bedescribed by the formula ##STR2## in which Ar is a C₆₋₂₀ aromaticmoiety, L is a cyclohexanenorbornane linking moiety, L' is a divalentcycloaliphatic moiety, and each of m and n is a number within the rangeof 0 to about 10. Such polyphenols include the product of the additionreaction of one or more phenols with a cyclohexenenorbornene such as5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene, and optionallydicyclopentadiene, in the presence of an addition catalyst such as borontrifluoride etherate. The resulting polyphenols are useful as curingagents for epoxy resins and as precursors of thermosetting resins suchas epoxy resins and cyanate ester resins.

DETAILED DESCRIPTION OF THE INVENTION

The invention polyphenols can be prepared by the addition reaction of aphenol with a cyclohexenenorbornene compound such as5-(3-cyclohexen-1yl)bicyclo[2.2.1]hept-2-ene. Suitable phenols includemono and polynuclear phenols having at least one unsubstituted positionortho- or para- to a phenolic hydroxyl group, such as phenol, cresol,3,4- and 3,5-dimethylphenol, resorcinol, biphenol, 1-naphthol andbisphenol A or F. Phenol is preferred.

Suitable cyclohexenenorbornene compounds include ##STR3## referred toherein as "monoadduct," "diadduct" and "triadduct," respectively, andisomers thereof.

The cyclohexenenorbornene is an adduct of 4-vinylcyclohexene andcyclopentadiene which can be prepared by contacting 4-vinylcyclohexeneand dicyclopentadiene, preferably in the presence of a polymerizationinhibitor such as t-butyl catechol, at a temperature of at least about180° C., preferably about 220° to 260° C., for a time within the rangeof about 2 hours to about 8 hours. Under these conditions, thedicyclopentadiene is cracked to cyclopentadiene, and thevinylcyclohexene and cyclopentadiene undergo an addition reaction toproduce a mixture of mono-, di- and poly-adducts along withcyclopentadiene oligomers (e.g., trimer, tetramer, pentamer, etc.). Thereaction product mixture containing predominately5-(3-cyclohexen-l-yl)-2-norbornene (monoadduct) is allowed to cool toabout 50°-70° C. and is stirred under reduced pressure to strip offunreacted vinylcyclohexene. The reaction product is then purified byfractional vacuum distillation to remove by-products including,optionally, di- and poly-adducts and cyclopentadiene oligomers, and thepurified product is passed through an adsorbent bed for removal oft-butyl catechol. Preparation of a vinylcyclohexene/cyclopentadieneadduct is illustrated in Example 1 herein.

The invention polyphenols can optionally include a residue L' of acyclic diene such as, for example, dicyclopentadiene, cyclopentadiene,norbornadiene dimer, norbornadiene, methylcyclopentadiene dimer,limonene, 1,3- and 1,5-cyclooctadiene, α- and y-terpinene,5-vinylnorbornene, 5-(3-propenyl)-2-norbornene, and cyclopentadieneoligomers. The preparation of such a phenol is illustrated in Example 4herein.

The phenol/adduct reaction is generally carried out by contacting, underaddition reaction conditions, the vinylcyclohexene/cyclopentadieneadduct and optional cyclic diene with a molar excess, preferably about10 to about 30 moles, of the selected phenol per mole of the adduct. Thereaction is most efficiently carried out in the presence of a Lewis acidaddition catalyst such as BF₃, coordination complexes thereof such asboron trifluoride etherate, AlCl₃, FeCl₃, SnCl₄, ZnCl₂, silica andsilica-alumina complexes and at an elevated temperature within the rangeof about 70° to about 200° C., preferably about 100° to about 180° C.The reaction is continued until the desired degree of reaction has beencompleted, usually for a time within the range of about 30 minutes toabout 10 hours, generally about 1 hour to about 3 hours. Preparation ofsuch polyphenols is illustrated in Examples 2, 4, 5 and 6 herein.

The invention phenolic compound can be combined with an epoxy resin by,for example, melt-blending, preferably in the presence of a curingcatalyst such as an imidazole. Subsequent cure of the epoxy resin iseffected by heating the epoxy/phenol mixture at a temperature aboveabout 150° C., preferably within the range of about 200° to about 300°C., for at least about 0.25 hour. Cure of epoxy resins with inventionphenols is illustrated in Examples 7, 8 and 9 herein.

The invention polyphenols are useful as curing agents for epoxy resins,as precursors for thermosettable resins such as epoxy resins and cyanateester resins, and as stabilizing additives for thermoplastics. Theinvention epoxy resin compositions are useful in molding powder, coatingand electrical encapsulation and laminating applications.

EXAMPLE 1

Preparation of 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene.

Dicyclopentadiene and 4-vinylcyclohexene in equimolar mixture wereheated in an autoclave at 240° C. for 4-4.5 hours. The reaction productwas diluted with cyclohexane and passed through a packed bed of aluminato remove the t-butylcatechol inhibitor introduced with the reactants.The resulting product mixture was distilled in a wiped film evaporatorat 3 mm Hg pressure at 90° C. to produce a light fraction containingunreacted vinylcyclohexene and dicyclopentadiene and the mono-adducts of4-vinylcyclohexene and cyclopentadiene. A 150 g sample of thisdistillate was vacuum distilled using a 10-tray Oldershaw column to givefour fractions. The fourth fraction, 65 g, was shown by gaschromatographic analysis to consist of 0.15% dicyclopentadiene, 88.3%endo-5-(3-cyclohexen-1-yl)-2-norbornene, 6.1%exo-5-(3-cyclohexen-1-yl)-2-norbornene and two additional componentspresent in the amount of 1.9% and 2.4% which are believed to be isomericadducts of the formula ##STR4## several additional components totallingabout 0.4%, 0.4% tricyclopentadiene and about 0.4% unidentifiedcomponents. Analysis of the fraction by nuclear magnetic resonanceindicated about 87 mole percent of the endo adduct, about 9 mole percentof the exo adduct and about 5% of the isomeric adducts.

EXAMPLE 2

Preparation of Polyphenol Based on 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene. To a reactor equipped with a stirrer, condensor andaddition funnel were added 188.2 g (2.0 mole) of phenol and 1.0 gBF₃.Et₂ O catalyst. The reaction mixture was heated to 70° C., and 17.4g (0.1 mole) of 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene was addedover a 20-minute period. The temperature was raised to 150° C. over a11/2-hour period and held for 21/2 hours. Unreacted phenol wasdistilled. The recovered product had a melting range of 70°-80° C., aphenolic hydroxyl content of 0.495 eq/100 g and a melt viscosity of 240cps (115° C.). The product polyphenol can be represented structurally as##STR5##

EXAMPLE 3

Preparation of Polyphenol Based on Dicyclopentadiene (Comparison). To areactor equipped with a stirrer, condensor and addition funnel wereadded 188.2 g (2.0 mole) of phenol and 1.Og of BF₃.Et₂ O catalyst. Thereaction mixture was heated to 70° C., and 13.2 g (0.1 mole) ofdicyclopentadiene was added over a 20-minute period and held for 21/2hours. Unreacted phenol was distilled. The recovered product had amelting range of 115°-120° C., a phenolic hydroxyl content of 0.62eq/100 g, and a melt viscosity of 635 cps (115° C.). The product can berepresented structurally as ##STR6##

EXAMPLE 4

Preparation of Polyphenol Based on5-(3-cyclohexen-1-yl)bicyclo[2.2..1]hept-2-ene/dicyclopentadiene. To areactor equipped with a stirrer, condensor and addition funnel wereadded 295.7 (3.14 mole) of phenol and 2.0 g of BF₃. Et₂) catalyst. Thereaction mixture was heated to 70° C., and 13.67 g (0.07856 mole) of5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene and 10.29 (0.07856 mole)of dicyclopentadiene were added over a 20-minute period. The temperaturewas raised to 150° C. over a 11/2-hour period and held for 21/2 hours.Unreacted phenol was distilled. The recovered product had a meltingrange of 70°-78° C. The product polyphenol includes repeating structuralunits ##STR7##

EXAMPLE 5

Preparation of Polyphenol Based on Vinylcyclohexene/CyclopentadieneDiadduct. To a reactor equipped with a stirrer, condensor and additionfunnel were added 376 g (4.0 mole) of phenol and 2.0 g of BF₃.Et₂)catalyst. The reaction mixture was heated to 70° C., and 48 g (0.2 mole)of diadduct was added over a 20-minute period. The temperature wasraised to 150° C. over a 11/2-hour period and held for about 21/2 hours.Unreacted phenol was distilled. The recovered product had a meltingrange of 85°-95° C. The product polyphenol can be representedstructurally as ##STR8##

EXAMPLE 6

Preparation of Polyphenol from Mixed Dienes. To a reactor equipped witha stirrer, condensor and addition funnel were added 376 g (4.0 mole) ofphenol and 2.0 g of BF₃.Et₂ O catalyst. The reaction mixture was heatedto 70° C., and 48 g of a diene mixture obtained from the Dieis-Alderreaction of cyclopentadiene and vinylcyclohexene were added over a20-minute period. The temperature was raised to 150° C. over a 11/2-hourperiod and held for 21/2 hours. Unreacted phenol was distilled. Therecovered product had a melting range of 87°-100° C. The productpolyphenol includes repeating structural units ##STR9##

EXAMPLE 7

Cure of Epoxy Resin. 27.5 g of a 67/33 (wt) blend of the diglycidylether of bisphenol A and tetrabromo-BPA, 4.8 g of the polyphenolprepared in Example 2 and O.03 g 2-imidazole were melt-blended at 150°C. The mixture was then heated at 250° C. for 20 minutes. The resultingcured epoxy resin had a Tg of 91° C.

EXAMPLE 8

Cure of Epoxy Resin. 27.5 g of a 67/33 (wt) blend of the diglycidylether of bisphenol A and tetrabromo-BPA, 4.7 g of the polyphenolprepared in Example 5 and 0.03 g 2-imidazole were melt-blended at 150°C. The mixture was then heated at 250° C. for 20 minutes. The resultingcured epoxy resin had a Tg of 91° C.

EXAMPLE 9

Cure of Epoxy Resin. 2 g of the tetraglycidyl ether of the tetraphenolof ethane, 2 g of the polyphenol prepared in Example 5 and 0.03 g of2-imidazole were melt-blended at 150° C. The mixture was then heated at250° C. for 20 minutes. The resulting cured epoxy resin had a Tg of 185°C.

EXAMPLE 10

Cure of Epoxy Resin (Comparison). 4.08 g of a 67/33 (wt) blend of thediglycidyl ether of bisphenol A and tetrabromo-BPA, 1.61 g of thepolyphenol prepared in Example 3, and 0.03 g of 2-imidazole weremelt-blended at 150° C. The mixture was then heated at 250° C. for 20minutes. The resulting cured epoxy resin had a Tg of 118° C.

We claim:
 1. A method for preparing a phenolic compound comprisingcontacting in a reaction mixture at least one cyclohexenenorbornenecompound and a molar excess of at least one phenolic compound in thepresence of a Lewis acid addition catalyst at a temperature within therange of about 70° to about 200° C.
 2. The method claim 1 in whichcyclohexenenorbornene compound comprises5-(3-cyclohexen-1-yl)bicyclo[2.2.1 ]hept-2-ene.
 3. The method of claim 2in which the phenolic compound is phenol.
 4. The method of claim 3 inwhich the catalyst comprises boron trifluoride.
 5. The method of claim 1in which the reaction mixture further comprises dicyclopentadiene.